An example of a modern, electronic weighing scale is the HAWK (.TM.) scale marketed by Pitney Bowes, Inc. of Stamford, Conn. Such a scale is capable of weighing articles, such as letters and parcels, and displaying their weight. Additionally, the scale is operable to calculate and display the monetary charge (e.g. postage) for posting or shipping each article. This is accomplished via rate data tables resident in the scale which are accessed by a microprocessor in the scale. These functions are well known and are accessible to the scale user via a keyboard. For example, a package is weighed and its weight is displayed. A carrier (shipper) is selected by the user and the microprocessor accesses the appropriate rate table to display the charge for shipping an article of that weight. In the interim a destination zone or zip code is typically entered via the keyboard, and may also be displayed by the scale.
Weighing letters as well as packages requires that the scale operate accurately over a wide range of applied loads (article weights). Thus it has been known to provide multirange postal/shipping scales. For example, U.S. Pat. No. 4,690,230 discloses a MULTI-RANGE LOAD CELL WEIGHING INSTRUMENT wherein, as shown in FIG. 4 therein, the output of a low range load cell is continuously monitored, but is not used for weight calculations in excess of 2.5 kilograms in which case the output of a high range load cell is employed. This dual load cell approach carries with it a premium--i.e., additional hardware and calibration costs.
The ultimate object of any multiranging scale is to provide at least two weighing "modes"; a high range mode such as 0-100 pounds, and a low range mode such as 0-10 pounds. However, in the high range mode it becomes extremely difficult to maintain accuracy while weighing at the lower end (near zero) of the high range mode. This problem becomes more poignant in the sale and use of scales which are regulated by state and local bureaus of weights and measures, and becomes more challenging when it is desired to employ low cost load cell technology.
In commonly-owned U.S. Pat. No. (Ser. No. 116936), entitled MULTIRANGING ELECTRONIC WEIGHING SCALE FOR TYPE-APPROVAL, and filed on Nov. 4, 1987 it is proposed that a manually-operable switch be employed on the scale to select between the high and low range weighing modes of operation for reasons pertaining to maintaining the value, d, of the interval between successive scale divisions constant across each of the two weighing ranges, without having d in the low range equal d in the high range. That patent application is hereby incorporated by reference.
In the context of such a manually-switched multiranging scale, the inventor has recognized that a user may, for example, neglect to switch the scale to the low range mode when weighing a lightweight article, such as letter, immediately after having weighed a heavier article, such as a parcel in the high range mode. This becomes a problem when the high range mode is not sufficiently accurate for lightweight letter mail.
Thus, it is an object of this invention to inhibit use of a manually switched multirange scale in the high range mode of operation for weighing lightweight articles, such as letters, thereby encouraging the user to switch to the low range mode for weighing such articles.